In recent years, it is a fashion for more and more people to use the series small-size decorative bulbs for ornamenting and beautifying the surroundings day after day. However, it is frequently heralded that the explosion of bulb because of over current burning out the filament leads to current leakage, short circuit or even anti-personnel accident. Therefore, the bulbs manufactures have to try various ways and means for improving such drawbacks. The present invention can achieve the objective of eliminating said drawbacks through a protective device of over current formed by the fuse seat.